Clonal relationship of tet(X4)-positive Escherichia coli ST761 isolates between animals and humans

Abstract

Objectives: To characterize the relationship of tet(X4)-positive isolates from different hosts and environments.

Methods: PCR and MALDI-TOF MS were used to identify the tet(X4)-positive isolates. The MICs of 13 antimicrobial agents were determined by broth microdilution. Illumina technology was used to sequence all of the isolates. One isolate was randomly selected from Escherichia coli ST761 clones for long-read sequencing to obtain plasmid sequences. Bioinformatics analysis was used to determine the phylogeny of 46 tet(X4)-positive E. coli ST761 strains.

Results: A total of 12 tet(X4)-positive isolates, 8 E. coli and 4 Aeromonas simiae, were obtained from six lairages of a slaughterhouse. These isolates exhibited resistance to at least three classes of antimicrobials, including tigecycline. The majority of them, seven E. coli and three A. simiae, represent separate clonal groups. Notably, the seven E. coli isolates belonged to ST761, a common ST carrying the tet(X4) gene that has been identified in 39 isolates from animals, meat, wastewater and humans from seven Chinese provinces. All 46 tet(X4)-positive E. coli ST761 strains from various sources have a close phylogenetic relationship (0-72 SNPs), with a high nucleotide sequence similarity of resistance genes and the tet(X4)-carrying IncX1-IncFIA(HI1)-IncFIB(K) hybrid plasmid, indicating a clonal relationship of tet(X4)-positive E. coli ST761 among animals, food, the environment and humans.

Conclusions: The clonal relationship of tet(X4)-positive E. coli ST761 between humans and animals poses a previously underestimated threat to public health. To the best of our knowledge, this is the first description of tet(X4)-positive A. simiae.